Copper absorption will be studied in terms of copper uptake by isolated intestinal cells from suckling mice, as whole animal or everted gut sac techniques are inappropriate in these animals. Preliminary studies have revealed isolated cell copper uptake is time- and concentration-dependent, depressed at low pH and OC, and is lower in cells from "crinkled" mice than from controls. These studies will be extended. We will also determine whether copper uptake is tissue-specific, related to brush border copper uptake and altered in conditions of high or low copper intake. A duodenal copper-binding protein (CuBP, MW approximately 10,000) has been isolated and its cooper-binding activity quantitated. Studies are proposed to determine whether this CuBP occurs or is altered in mice with the autosomal allele "crinkled" or the sex-linked allele "mottled (brindled)" and whether high or low copper intakes affect CuBP levels. The duodenal, cytosolic CuBP will be compared to other non-metallothionein copper-binding proteins and brush borders and other tissues will be analyzed for CuBP.